1) Field of the Invention
This invention relates generally to fabrication of magnetoresistive (MR) heads, and more particularly a method to align a step and repeat exposure tool (reticles) on sliders for MR heads and more particularly to a step and repeat exposure process using three wafer alignment marks for two adjacent exposure fields.
2) Description of the Prior Art
Thin film head magnetoresistive (MR) elements are printed using a step and repeat system in rows that eventually require the magnetoresistive (MR) stripe on all devices in the two inch row (equivalent to two adjacent stepper flash fields) be lapped simultaneously to a specific height. The inventors have found inaccuracies in the stepper stage position (rotation and shift from expected position) when stepping the adjacent image fields creates a step function within the row bar. The devices along the two inch row bar should "line up" perfectly to allow optimum lapping conditions. The step function at the row center causes yield fallout due to poor magnetoresistive (MR) resistance because the lapping process cannot accommodate the step perfectly. The step function error has been typically measured by the inventors as 130 nm one sigma when aligning the image fields at the stepper using conventional independent alignment targets.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering U.S. Pat. No. 4,823,012(Kosugi) shows a step and repeat system having alignment marks provided in association with neighboring fields on the wafer which are to be exposed to the reticle pattern in sequence.
U.S. Pat. No. 5,695,897(Mitome et al.) shows an alignment method where two steppers have different reduction magnification is used to perform a global alignment and a smaller field alignment.
U.S. Pat. No. 5,716,889(Tsuji et al.) and U.S. Pat. No. 5,250,983(Yamamura) show alignment marks in the kerf between dies.
U.S. Pat. No. 5,733,690(Jeong et al.) shows two sets of alignment marks formed on the scribe line to measure overlay.
U.S. Pat. No. 4,982,227(Suzuki) shows a method for alignment using multiple alignment modes by adapting an alignment method by a sample alignment prior to the exposure operation. The alignment modes examines multiple sized fields.